can somebody explain this

[scole]

what is the grn/yel wire from the power transformer to the 220k and the 33k, .01 cap doing?

[NorCalTuna]

an idea

I'm thinking it's the center tap of the heater windings, and the cap bypass resistor forms a voltage divider which supplies it at a ratio of 33/220. So, if it's b+ is 450, it'll float the heaters to 67.5v. I think.

[tubeswell]

Yep heater elevation, which doubles as a filter cap bleeder circuit. Incidentally the .01uF cap would probably be better at 8uF or 10uF (say 100V) to effectively take out any otherwise possible oscillation.

[scole]

so does that 220k need to be 3watt or 2 watt enough?

[tubeswell]

Assuming the B+ is 450, the voltage at the knee is:

33k/(220k +33k) = 0.13 =~ 13% (of 450V) = 58.69V (say 59V)

Therefore the voltage dropped across the 220k is:

450 - 59 = 391V

Therefore the power dissipated by the 220k is:

(391V/220000R) x 391V = 0.00177727272727A x 391V = 0.695W

therefore 2W would be more than sufficient